1. Technical Field
The present invention relates to a vacuum type heat-treating furnace, and more particularly, to a double-chamber type heat-treating furnace.
2. Description of the Related Art
A vacuum type heat-treating furnace is a heat-treating furnace in which heat treatment is applied to an object to be treated (hereinafter referred to as an object) after re-filling of inert gas therein subsequent to a reduction in its internal pressure. In the vacuum type heat-treating furnace, when moisture is attached to the inside of the furnace and the object after heating the furnace per se, and when the moisture is gasified, since the furnace can be again depressurized to subsequently accomplish re-filling of the inert gas thereby completely removing moisture component from the furnace, there is such a merit that heat treatment with no coloring by moisture (it will hereinafter be referred to as “bright heat treatment”) can be effected.
Further, a gas-cooling type vacuum heat-treating furnace can carries out bright heat treatment and also, can enjoy various advantages such as no occurrence of decarburizing or carburizing, a less deformation, and acquirement of improved working environment. However, the gas-cooling type vacuum heat-treating furnace during the initial stage employs pressure-reduction cooling system. Thus, it must be encountered by such a defect that cooling speed is insufficient. Therefore, to increase the cooling speed, a high-speed-circulation type gas-cooling system has come into practical use.
FIG. 1 is a general configuration of a high-speed-circulation gas-cooling furnace as disclosed in non-patent publication 1. In this drawing, reference numeral 50 designates heat-insulating material, 51 a heater, 52 an effective working area, 53 a furnace body and a water-cooling jacket, 54 a heat-exchanging device, 55 a turbo fan, 56 a fan-motor, 57 a cooling door, 58 a furnace floor, and 59 a gas-distributor.
Further, the patent document 1 discloses “a method of promoting gas-circulation cooling in a vacuumed furnace”. In the vacuumed furnace, as illustrated in FIG. 2, heating chamber 66 surrounded by heat-insulating walls 67 is provided within hermetically sealed vacuum container 61, so that heater 62 disposed in the heating chamber heats heated object 64 in vacuum environment. In addition, cooler 62 and fan 63 are disposed in the vacuum container 61, so that non-oxidizing gas supplied into the vacuum container is cooled by cooler 62 and is introduced, due to the rotation of fan 63, into heating chamber 66 through openings 68 and 69 provided in respective faces of opposing heat-insulating walls 67 to be circulated within the heating chamber 66 so as to forcibly applying gas-cooling by circulation to the heated object 64. In the described vacuumed furnace, heat-resistant cylindrically-shaped hood 65 having at least one end formed in a divergent shape is disposed so as to surround the circumference of heated object 64, which is positioned within heating chamber 66, with an appropriate space therebetween, and the opposite ends of the hood are arranged to oppose to the above-mentioned openings 68 and 69 so that the non-oxidizing gas is circulated within heating chamber 66.
On the other hand, the patent document 2 is known which discloses a double-chamber type heat-treating furnace in which heating and cooling are carried out in separate zones.
The “multi-chamber type heat-treating furnace” of the patent document 2, which is, as illustrated in FIG. 3, formed with a gas-cooling chamber and a heating chamber sectioned by an intermediate door, is provided with, at openings 72a and 72b disposed on opposite sides of gas-cooling chamber 71 for passing therethrough a material to be treated, clutch-system hermetically closable door 73 and 74, thereby forming the gas-cooling chamber in a pressure-resistant structure. In addition, at least clutch-system hermetically closable door 74 on the side of heating chamber 75 is structured to have an elevating system, and heat-insulating door 78 is disposed at the material-passing opening of the heating chamber so that heat-insulating door 78 and clutch-system hermetically closable door 74 on the side of the heating chamber are arranged within door-hood 79, which is provided between heating chamber 75 and gas-cooling chamber 71.
[Non-patent Document 1]
Heat Treatment volume 30, No.2, Vacuum Heat Treatment of Metallic Materials (2) written by Katsuhiro YAMAZAKI, April, H2 (1990)
[Patent Document 1]
Japanese Unexamined Patent Publication No. H5-230528
[Patent Document 2]
Japanese Patent Publication No. 2731127
The high-speed circulation-gas cooling furnace disclosed by the non-patent document 1 and the patent document 1 is constructed so that heating and cooling operations are performed in the same zone and therefore, there have been problems as follows.
(1) The heater for heating-purpose and the furnace body are at a high temperature condition at completion of heating operation and accordingly, the heater and the furnace body must be cooled simultaneously at the time of cooling operation. Thus, rapid cooling of the object to be treated cannot be achieved.
(2) The heater for heating purpose and the furnace body are arranged so as to surround the object to be treated and therefore, the cooling gas cannot be evenly supplied at the time of cooling operation.
Further, in the double-chamber type heat-treating furnace disclosed by the Patent document 2 heating and cooling operations are performed in the separate zones and therefore, the problems (1) and (2), above can be eliminated. However, there is still a problem as follows.
(3) In the double-chamber vacuum heat-treating furnace, a transfer mechanism for transferring objects to be treated between heating and cooling chambers is indispensable. This transfer mechanism is comprised of a roll-conveyer supporting, for example, the lower face of the object to be treated, and horizontally moving same.
Nevertheless, when this mechanism is disposed under the objects to be treated within the cooling chamber, smooth flow of the gas within the cooling chamber is hindered to render the flow of the gas complicated and accordingly, the cooling gas cannot be evenly supplied to the objects to be treated.
Moreover, even when the transfer mechanisms are arranged on respective sides of the heating/cooling chambers, drive rollers act to form a partial block, for example, over a width of the chambers in direction and therefore, the cooling gas cannot be equally supplied upwardly and downwardly to the objects to be treated. Further, if a drive mechanism is disposed in the heating chamber, protections against heat to the drive mechanism is indispensable, and as a result, the drive mechanism must become complicated.